1. Field of the Invention
The present invention relates to electronic siren circuits and more particularly is an improved electronic siren circuit incorporating a square wave generator and an output circuit which utilizes diffused based transistors having a fast "rise" time and which are driven sharply between non-conducting and saturated states whereby heat and power losses within the circuit are minimized.
2. Description of the Prior Art
Prior art electronic siren circuits, such as that disclosed in U.S. Pat. No. 3,051,944 to the present Inventor, typically include a voltage controlled variable frequency oscillator which generates a square wave output signal, the square wave having a repetition rate or frequency in the audio frequency range. These circuits further include voltage signal generating circuits which apply a selected one of a plurality of different wave forms to the variable frequency oscillator to produce the desired siren signal. The output of the voltage controlled variable frequency oscillator is then applied to a speaker through a suitable power amplifier.
In the majority of applications, the electronic siren is installed in a motor vehicle or similar mobile unit. Consequently, the power and space available to operate and install the siren is limited. For this reason, and due to the need to produce a siren sound having a sufficient volume to be heard above normal ambient sound levels, it is important that the siren circuit produce the desired siren sounds with maximum efficiency. In this regard, prior art electronic siren circuits exhibit some loss of efficiency which results from rounding off of the square wave sound-generating signals produced therein.